This paper delineates the organizational structure and operational procedures of the Michigan Institute for Educational Management (MIEM) Assessment Center Program for prospective school principals and assistant principals. The program is part of the Assessment Center Project of the National Association of Secondary School Principals (NASSP). The primary program purposes are to improve leadership quality at the school building level and to promote improved training programs for principals. The center diagnoses each candidate's strengths and weaknesses in 12 skill dimensions required for effective principal performance by observing simulated activities and through personal interviews. Assessment results are reported to the candidates and the sponsoring school districts. Twelve school districts' candidates meeting eligibility requirements are selected for each assessment session. The Assessment Center program is directed by the Assessment Center Director and the Coordinating Council. Program implementation involves the partnership of the NASSP, the Michigan Department of Education, MIEM, public school districts and educational consortia. Assessors are carefully selected and trained. Report security, assessment materials, program monitoring, schedule, location, operational documents, and program evaluation are also discussed. (BS)